import java.util.Scanner;

/**
 * @author yu
 * @date 2025年04月17日 9:28
 */
public class _09_dp_02_70climbStairs {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        int n = scanner.nextInt();
        System.out.println(climbStairs(n));
        scanner.close();
    }
    public static int climbStairs(int n){
        if(n < 3) return n;
        int[] dp = new int[n+1];
        dp[1] = 1;dp[2] = 2;
        for(int i = 3 ;i < n+1; i++){
            dp[i] = dp[i-1]+dp[i-2];
        }
        return dp[n];
    }
}
